Multi-cylinder internal combustion engine with variable actuation of the engine valves

ABSTRACT

In a multi-cylinder internal combustion engine, valves of the engine, in particular the exhaust valves ( 3 ), are actuated by rocker arms ( 18 ) each of which is rotatably mounted on the structure of the engine with the interposition of an eccentric bushing ( 39 ), whose rotation allows varying the position of the rotational axis of the respective rocker arm, so as to activate and deactivate an extra-lift of the engine valve. The eccentric bushings ( 38 ) associated to the rocker arms ( 18 ) of the various cylinders of the engine are all connected in rotation with a common shaft ( 100 ) which is rotatably supported on the structure of the engine and which can be rotated through actuator means ( 105 ) preferably arranged outside the engine.

FIELD OF THE INVENTION AND PRIOR ART

The present invention refers to multi-cylinder internal combustionengines of the type indicated in the preamble of the attached claim 1.Engines of this type are illustrated in documents EP 0 543 210 B1, EP 1927 734 A2 and EP 1 927 735 A1.

Compression braking systems for internal combustion engines, inparticular for reciprocating engines such as diesel engines for heavyduty vehicles, are known. In these engines compression braking allowsattaining extremely high specific braking powers, especiallysimultaneously with a supercharging performed by means of turbochargerswith variable geometry.

It is known that such systems provide for a supplementary opening of thecylinder exhaust valve during braking, to avoid the expansion of the airin the cylinder after the compression stage, thus reducing the brakingefficiency.

In order to attain such results there have been proposed various typesof devices, among which in particular devices for varying the positionof the rotational axis of the rocker arms which control the opening ofexhaust valves.

FIG. 1 of the attached drawings shows the solution known from EP 0 543210 B1. In such figure, number 1 is used to—generally designate amulti-cylinder internal combustion engine, in particular a turbochargeddiesel engine, comprising—for each cylinder—a combustion chamber (notshown in the drawing) with at least one intake conduit (also not shownin the drawing) and at least one exhaust conduit (the illustratedexample shows two exhaust conduits 9 converging into an exhaust manifold10). According to the conventional art, associated to the exhaustconduits 9 are exhaust valves 3 biassed by respective springs 13 towardsan upper (with reference to the drawing) closed position of therespective conduits. The engine further comprises, still according tothe conventional art, at least one camshaft with cams 36 for controllingthe valves, which for example can be a single camshaft intended tocontrol both the intake valves and the exhaust valves. Each exhaustvalve 3 of each engine cylinder is displaceable towards a lowered (withreference to FIG. 1) position for opening the respective exhaustconduit, against the action of the respective spring 13, by a rocker arm18 rotatably mounted around a rotation axis O on the structure of theengine. The rocker arm 18 has one end freely rotatably supporting aroller 27 which cooperates with a respective cam 36 of the camshaft. Theother end of the rocker arm controls the displacement of the two exhaustvalves 3 associated to each cylinder, by means of a bridge-likestructure (naturally a single exhaust valve for each cylinder mayobviously be provided which is controlled directly by the end of therespective rocker arm).

Still according to the abovementioned prior art solution, the cam 36 hasa main lobe 58 to obtain the lifting of the exhaust valves during theexhaust stage of the operating cycle of the respective cylinder, a zerolift portion 56, which does not determine any lift of the exhaustvalves, and a portion 57 slightly lifted with respect to the circularbase profile for attaining a slight extra lift of the exhaust valvesduring the compression stage in the respective cylinder, which extralift is actuated—simultaneously with an interruption of fuel supply tothe combustion chamber—when an engine braking effect is requested.

Still according to the known solution illustrated in FIG. 1, the rockerarm 18 is rotatably mounted on a fixed axle onto the structure of theengine with the interposition of an eccentric bushing 39 whose angularposition around the support axis may be varied. In the specific case ofthe illustrated example, this is done through a fluid actuator 46, alsoillustrated in FIG. 1, which operates on a lever 45 connected inrotation with the bushing 39. The variation of the angular position ofthe bushing 39 determines a variation of the position of the rotationaxis of the rocker arm 18 with respect to the structure of the engine.When the engine-braking effect is not required, the position of therotation axis of the rocker arm is selected in such a manner that thearm 18 is unaffected, due to the existing clearance, by the portion 57of the profile of the cam 36, thus the extra-lift of the exhaust valvesis not activated during the cylinder compression stage. On the contrary,when one wants to obtain the engine braking effect, the supply of fuelto the cylinders is cut off and the eccentric bushings 39 of the variousrocker members are rotated in such a manner that the latter “feel” theprofile 57 and cause the abovementioned extra-lift. In such manner, thebraking effect caused by the engine during the compression stage of eachcylinder is not jeopardised by an elastic re-expansion of the air in thecylinder during the subsequent stroke of the piston towards the BottomDead Centre, in that at least part of the air has been evacuated fromthe cylinder in the meanwhile.

DRAWBACKS OF THE PRIOR ART

Though guaranteeing the advantages indicated above, the aforedescribedprior art device is not entirely satisfactory in terms of simplicity andcost of manufacture. Further devices of this type have been proposed inEP 1 927 734 A2 and EP 1 927 735 A1 in the attempt to simplify andreduce the number of required components but they are yet to attain anactually satisfactory result.

OBJECT OF THE INVENTION

The object of the present invention is that of proposing a device of theaforedescribed type capable of allowing a dramatic simplification of thedevice itself with respect to those proposed previously and an ensuingdramatic reduction of the production costs.

SUMMARY OF THE INVENTION

The main characteristic of the invention is indicated in thecharacterizing part of the attached claim 1.

As visible, the invention provides for, equivalently to the prior artsolution described above, that the rocker arms associated to the valves(in particular to the exhaust valves) of the various cylinders of theengine be rotatably supported by interposing eccentric bushings, whichmay be rotated to vary the position of the rotational axis of the rockerarms.

However, the eccentric bushings are not rotatably mounted each on arespective fixed axle, but rather they are connected in rotation on acommon shaft which is rotatably supported by the structure of theengine.

Due to this kind of solution, the adjustment of the angular position ofall the eccentric bushings associated to the various cylinders of theengine may be obtained simultaneously, through actuator means of anytype suitable to rotate the abovementioned common shaft to which theeccentric bushings are connected in rotation.

For example, among various types of actuator means, a hydraulicallycontrolled actuator device may be provided of a type similar toconventional devices used for adjusting the camshaft phase, comprising arotor connected in rotation with the shaft supporting the eccentricbushings, and a stator fixed onto the structure of the engine andsurrounding the rotor, with hydraulic means for the variation of theangular position of the rotor with respect to the stator. In any case,it is surely possible to use actuators of any other type, such ashydraulic, electric or pneumatic actuators, or also a transmissionbetween the actuator means and the driven shaft, to increase thetransmitted torque, for example a crank connected to the shaftsupporting the eccentric bushings and actuated by a fluid linearactuator, or a gear transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will becomeapparent from the description that follows with reference to theattached drawings, provided strictly for exemplifying and non-limitingpurposes, wherein:

FIG. 1 illustrates the device for controlling the exhaust valves of acylinder of an internal combustion engine according to the art knownfrom EP 0 543 210 B1,

FIG. 2 is a schematic perspective view illustrating the base principleof the present invention,

FIG. 3 is a further schematic perspective view of the device accordingto the invention, and

FIG. 4 is a diagram of a possible example of an actuator used in thedevice according to the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The prior art solution illustrated in FIG. 1 has already been describedabove. The main difference of the present invention with respect to suchknown solution is immediately evincible from FIG. 2 of the attacheddrawings. Such difference essentially lies in the fact that theeccentric bushings 39 associated to the rocker arms 18 for the actuationof the exhaust valves of the various cylinders of the engine areconnected in rotation to a common shaft 100, instead of being freelyrotatably mounted on respective axles. In the case of the embodimentillustrated in FIG. 2, the bushings 39 are connected in rotation on theshaft 100 by means of transverse pins 101 engaging diametric holesformed through the shaft 100 and corresponding holes diametricallyopposite with respect to each other formed on each bushing 39. It ishowever clear that any other type of connection may be used.

Likewise, the embodiment visible in the drawings shows that the shaft100 is rotatably supported by the structure of the engine withinrespective seats 102 which are defined partly by supports 103 formingpart of the structure of the cylinder head of the engine and partly bycaps 104 (only one of which is visible in the drawings) fixed by meansof screws 104 a (FIG. 3) to the supports 103. Preferably low frictionsupport bearings are provided in the seats in which the shaft 100 ismounted.

Due to the abovementioned characteristic, the device according to theinvention enables simultaneous adjustment of the angular position of allthe eccentric bushings 39, in order to obtain the activation anddeactivation of the extra-lift of the exhaust valves which has beendiscussed above with reference to figure 1, by simply controlling arotation of the common shaft 100 to which the eccentric bushings 39 arefixed.

As previously indicated, the actuator means used for controlling therotation of the shaft 100 may be of any type. In the case of the exampleillustrated in the attached drawings, a hydraulically controlledactuator is procided of a type similar to that used conventionally usedfor adjusting the camshaft phase. According to this art, known per se,the actuator, generally designated by reference number 105, comprises arotor 106 with blades 106 a which is connected in rotation with theshaft 100 and rotates within a circular stator 107 with internal blades107 a. As better visible in FIG. 4, defined between the rotor 106 andstator 107 are hydraulic chambers which are selectively connected to asupply pump 108 and a reservoir 109 through a control valve 110, in sucha manner to control the adjustment of the angular position of the shaft100 and hence of the eccentric bushings 39.

As clearly apparent from the foregoing description, the device accordingto the invention allows using one actuator for simultaneouslycontrolling the adjusting of the position of the rocker members 18controlling the exhaust valves of the engine cylinders. Not only is thedevice extremely simple and inexpensive to manufacture but it alsoallows a considerable reduction of the number of components with respectto the solutions proposed previously. The device according to theinvention also allows easily positioning the actuator device evenoutside the engine, with the ensuing advantages even in terms ofreducing the temperature and vibrations to which the actuator issubjected and thus also avoiding any restrictions regarding thedimensions of the actuator and/or the type of actuator one intends touse.

As indicated severally, the means for actuating the rotation of theshaft 100 for supporting the eccentric bushings 39 may be of any type,and in particular they may be of pneumatic type, hydraulic type orelectric type.

Furthermore, the device according to the invention would be identicallyapplicable even to distribution systems using a different kinematicchain for controlling the valves, with levers of a different type withrespect to the rocker arms indicated herein. Therefore, in the claimsthat follow, the term “rocker arm” shall be considered to include thecase of any lever having a rotational movement around one axis.

Additionally, as previously indicated, a further preferred example ofactuator means could be made up of a linear hydraulic actuator connectedto a crank lever connected to the shaft 100. A mechanical transmission(for example a linkage or a gearing) may be generally interposed toincrease the torque transmitted to the shaft 100.

It should also be observed that the eccentric bushings 39 may be eachformed in a single piece or also in several pieces connected to eachother. Furthermore, should the rocker arms that control the intakevalves be mounted on the same rotational axis of the rocker arms whichcontrol the exhaust valves, the intake rocker arms may be freelyrotatatably mounted on the abovementioned common support shaft 100, insuch a manner to be unaffected by the rotations of the latter.

Furthermore, the invention is obviously also theoretically applicable todevices for actuating the intake valves of the engine, in any desiredcase in which, for any reason, it is required to activate or de-activatean extra-lift of the intake valves through simple and inexpensive means.Lastly, the device is also applicable in any other case in which onedesires to obtain an extra-lift of the exhaust valves, to obtain effectsdifferent from that of compression braking.

Naturally, without prejudice to the principle of the invention, thedetails and embodiments may vary, even significantly, with respect towhat has been described and illustrated strictly for exemplificationpurposes, without departing from the scope of the present invention.

1. Multi-cylinder internal combustion engine, comprising, for eachcylinder, a combustion chamber with at least one intake conduit and atleast one exhaust conduit intake valves and exhaust valves associated tosaid conduits and biassed by spring means towards a closed condition ofthe respective conduit, at least one camshaft for controlling theabovementioned valves, each valve being movable towards an openedcondition of the respective conduit, against the action of therespective spring means, by a cam of the abovementioned camshaft bymeans of a mechanical transmission including a rocker arm rotatablymounted on the structure of the engine, wherein each of the rocker armsassociated to the exhaust or intake valves of the engine is rotatablymounted on the structure of the engine with the interposition of aneccentric bushing, and wherein actuator means are provided for rotatingthe abovementioned eccentric bushings associated to the rocker armscontrolling the valves of the various cylinders, to vary the position ofthe rotation axis of the rocker arms, characterised in that theabovementioned eccentric bushings associated to the rocker arms of thevarious cylinders of the engine are all connected in rotation with acommon support shaft which is rotatably supported on the structure ofthe engine, and in that said actuator means are arranged to control arotation of the abovementioned common support shaft.
 2. Engine accordingto claim 1, characterised in that said actuator means are positionedoutside the structure of the engine.
 3. Engine according to claim 1,characterised in that said actuator means are chosen among actuatormeans of the pneumatic type, actuator means of the electric type andactuator means of the hydraulic type.
 4. Engine according to claim 1,characterised in that interposed between the actuator means and theabovementioned common support shaft is a mechanical transmission, suchas a linkage or a gearing.
 5. Engine according to claim 1, characterisedin that the abovementioned common support shaft is rotatably supportedwithin seats partly defined by supports forming part of the cylinderhead of the engine and partly by caps fixed onto said supports. 6.Engine according to claim 1, characterised in that said actuator meansare hydraulically controlled actuator means, including a rotor connectedin rotation with said common support shaft and rotatable within a statorfixed onto the structure of the engine, said stator and rotor defininghydraulic chambers therebetween which can be selectively connected bymeans of a control valve to a hydraulic supply and a reservoir. 7.Vehicle, in particular an industrial vehicle, characterised in that ithas an engine according to claim 1.